1. Field of the Invention
The present invention relates to a transmitter apparatus for transmitting a RF (radio frequency) pulse signal, a transmitter/receiver apparatus incorporating the transmitter apparatus, and a receiver apparatus for receiving signals that have been transmitted by a RF pulse signal transmitter apparatus.
2. Description of Related Technology
Types of transmitter apparatus are known (e.g., for radar applications) which incorporate an array antenna having a plurality of antenna elements, wherein an RF pulse signal is supplied as respective individual transmission signals to the antenna elements, with the phase distribution (combination of phases) of the individual transmission signals being predetermined for transmitting the RF pulse signal as a beam of modulated electromagnetic waves in a specific direction. The term “RF pulse signal” as used herein signifies a signal (as illustrated by the waveform diagram of FIG. 12), generated by a known type of pulse modulator circuit. The signal consists of intervals (Pon) of high-amplitude RF signal (referred to herein as the “pulse-on” condition) separated by intervals (Poff) of low-amplitude RF signal (referred to herein as the “pulse-off” condition).
With a practical type of pulse modulator circuit for generating such a signal at high RF frequencies, it is not possible to completely exclude a RF signal component during the pulse-off condition. The low-amplitude RF signal in the pulse-off condition is referred to in the following as the leakage signal component.
It is desirable that the amplitude ratio of the pulse-on to pulse-off portions (i.e., ratio of amplitude in pulse-on condition to the leakage signal amplitude) should be sufficiently high. However that has been difficult to achieve hitherto. To try to reduce the relative amplitude of the leakage signal component it has been proposed (for example in International patent publication No. 2006/059367) to incorporate a switch, which will be controlled to pass each pulse-on portion of the RF pulse signal and to block each pulse-off portion. It is further proposed to incorporate an amplifier for amplifying the RF pulse signal only during each of the pulse-on intervals.
However such methods of improving the transmitting/receiving performance by reducing the relative amplitude of the leakage signal component have the disadvantage of requiring expensive additional devices such as switches and amplifiers.